Field of the Invention--This invention relates to a torque transfer assembly and, more specifically, to a drive transfer assembly for a four-wheel drive vehicle.
Description of the Prior Art--Transfer assemblies providing four-wheel drive capability are desirable for many vehicles which are used on rough terrain as well as on relatively smooth surfaced roadways. Four-wheel drive utility vehicles are commercially available and relatively well known. The four-wheel drive is used primarily as the vehicle is traveling, normally at a higher rate of speed, on a surfaced roadway.
In such vehicles the rear axle normally serves as a primary driving axle and the front axle serves as an auxiliary driving axle when the wheels on the rear axle fail to provide the desired traction. The transfer of torque from the primary driving axle to the auxiliary driving axle may be effected automatically or by manual operation.
As in conventional driving axles, both the primary and the auxiliary driving axles are provided with differentials to accommodate differences in the speed of rotation of the wheels at each end of a single axle. In a four-wheel drive vehicle it is also necessary to accommodate different speeds of rotation between the wheels mounted on the primary driving axle and the wheels mounted on the auxiliary driving axle. Such wheel speed differences between the axles may occur as a result of a difference in the effective diameter of the front and rear wheels due to the vehicle load, a difference in the length of the arcuate paths traveled by the front and rear wheels while negotiating a turn, or by one set of wheels spinning or stopping due to the loss of friction or an obstacle in the path of travel.
The inter-axle wheel speed differential may be accommodated by the torque or drive transfer mechanism. U.S. Pat. Nos. 2,331,908 and 2,105,918 to J. E. Henningsen and A. W. Herrington, respectively, both disclose a transfer case including a gear axially movable in response to an increase in the rotary speed of one of the driven axles and thereby interrupts the four-wheel drive by disengaging a pair of gears transmitting torque to the auxiliary axle. Other four-wheel drive mechanisms are disclosed in U.S. Pat. Nos. 2,711,222, 3,295,625 and 3,481,436 respectively issued to C. J. Bock, N. A. Ordorica et al. and E. A. Wilkowski.
The transfer mechanisms disclosed in the foregoing patents involve an assembly in which the torque is transferred from the input to the output shafts by means of gears mounted on an intermediate or countershaft. These prior art assemblies are thus comprised of at least three levels which are satisfactory for mounting on many over-the-road and off-highway vehicles having adequate ground clearance to accommodate the depending transfer case and propeller shafts tranferring torque from the case to the drive axles. However, the size and dimensions of the prior art transfer cases are such that they are not readily adaptable to equipment requiring a low profile such as the vehicles utilized in underground mining operations.
U.S. Pat. Nos. 3,557,634 and 3,679,016 to L. A. Bixby disclose a differential transfer assembly in which the primary and auxiliary driving axles are driven from the same power shaft but that design requires two sets of drop gears, one in front and one to the rear of the differential, and a power shaft traversing the differential housing.